1. Technical Field
The present invention relates to a time adjustment device that corrects the time based on signals from positioning information satellites such as GPS satellites, to a timekeeping device having the time adjustment device, and to a time adjustment method.
2. Related Art
GPS satellites that circle the Earth on known orbits are used in the Global Positioning System (GPS), which is a system for determining one's location, and each GPS satellite carries an atomic clock. Each GPS satellite therefore maintains extremely accurate time information (referred to herein as satellite time information).
Electronic timepieces that adjust the time using time information (satellite time information) from GPS satellites are also known from the literature. See, for example, Japanese Unexamined Patent Appl. Pub. JP-A-2009-145318.
JP-A-2009-145318 describes a device that can select either of two reception modes, a first mode that receives first information composed of the hour-minute-second (Z count) information from the satellite signal, and a second mode that receives second information containing hour-minute-second information, week information including the year, month, and day, and satellite health information.
Once the time has been adjusted using the second information, the time is subsequently adjusted by receiving only the first information, but if the time has not adjusted using the second information, the second information is received to adjust the time.
As a result, only the first information needs to be received once the time has been adjusted using the second information. Time information can therefore be received in a short time compared with when the second information is received, and power consumption can be reduced.
The time information (satellite time information) received from a GPS satellite does not reflect leap seconds, and UTC (Universal Coordinated Time) must therefore be acquired by adding the cumulative leap seconds.
In JP-A-2009-145318, this cumulative leap second value is fixed. As a result, when the leap second count is updated and added to UTC, the internal time of the timepiece will differ from UTC and the correct time cannot be displayed.
Current leap second information is carried in subframe 4, page 18 of the GPS signal, and the correct time can be set if this leap second information is received.
However, the leap second information is transmitted every 12.5 minutes, and the reception process must continue for at most 12.5 minutes in order to receive the leap second information when adjusting the time.
The reception process therefore takes longer and power consumption increases, thus shortening the duration time of small mobile devices with low battery capacity, such as wristwatches.